CLASSIFICATION OP THE MAIOID CEUSTACEA. 667 



there being no tnbercles or spines on tlie lateral margins of the 

 carapace and very obscurely marked tubercles on the branchial 

 regions. The orbital margins, also, are smooth. The much dilated 

 basal antennal joint has a single spine at its extero-distal angle ; 

 the legs are smooth.) 



Thoe, JBell (Platt/pes, Lockington). Carapace triangular, 

 narrowed anteriorly. Eostrum very short, its spines reduced to 

 tubercles. Basal antennal joint witli a very short spine at its 

 distal end. Anterior legs in male enlarged, palms short, dilated, 

 fingers meeting only at tips. Ambulatory legs compressed and 

 dilated. Type TJioe erosa, Bell. 



MiTHRAx, Leach. (Plate XIII. figs. 7, 8.) Carapace broadly 

 triangular, usually transverse. Spines of rostrum short or 

 obsolete. Basal antennal joint dilated, with short spines at its 

 distal end. Anterior legs in male usually enlarged. Ambulatory 

 legs not dilated and compressed. 



Subgenus Mitheas, Leach {Teleophrys, Stimpson), Carapace 

 with the branchial regions not sulcated, sides usually spinose. 



Subgenus Mitheactjltjs, White. Carapace depressed, with 

 shallow smootb interspaces or sulci between the tubercles on the 

 branchial regions, antero-lateral margins tuberculate (anterior 

 legs greatly enlarged). Type Hithracidus sculptus (Lamarck). 



Scarcely distinct even as a subgenus from Mithrax, although of 

 very different external aspect ; the characters of the orbital and 

 antennal region are not constant. Teleophrys of Stimpson marks 

 the transition from Mithrax to Mithraculus. 



Family IV. PARTHENOPIDiE. {Parthenopiens and Canceriens crypto^ 

 podes, M.-Edwards). 



Eyes usually retractile within the small circular and well-defined orbits ; 

 the inferior wall of the orbit is continued to within a very short 

 distance of the front. The antennte are very slender, the basal joint 

 does not, as in the PericeridEe, constitute a great part of the interior 

 orbital margin, but is very small, and usually does not reach to the 

 front, and with the next joint occupies the narrow hiatus intervening 

 between the front and inner orbital angle. 



The structural relationship of this family with the Oxystomata, 

 best evidenced in the genus Mesorhcea, has been already adverted 

 to ; and there are resemblances also in external characters, such 

 as the lateral extension of the carapace over the ambulatory legs 



